Emerald crab safe with pom pom crab
 

I got a small pom pom crab about a month ago for my tank I never saw it so I thought is was dead and forgot about it last week I had a hair algae outbreak and got some emerald crabs the last night I saw the pom pom crab out and very healthy and started to worry that a emerald crab might eat it do you think it's safe

Glad you got to see your pom pom. I put one in about a month ago and it has been MIA ever since. My guess is that if the emeralds were going to get they would have already done so.

I personally do not trust emerald crabs.

i saw it the night after i got the crabs

Usually these crabs can be kept together. The Mithraculus species are primarily algae eaters that don't prey on other crabs. They surely would feed on a freshly molted Lybia if it couldn't hide well in the tank.